Hydrofining of middle distillate feed stock



Aug. 29, 1961 J. D. BUSHNELL HYDROFINING OF MIDDLE DISTILLATE FEED STOCK Filed Sept. 22, 1958 w 555m 52 58.5 55%. 2 MW 538% 2 LN N 55556 58;. m. ON m5 255 N: mmm zm w mokuqmm .5385 585 5 mm pm :55

F "Eng? 3 8 m jmobfimw En z 35, in mm mm mm F 1. mm T mi 98 mm 15m NEE Inventor James D. Bushnell nited States Patent 2,998,381 HYDRUFINING 0F MIDDLE DISTILLATE FEED STOCK James D. Bushnell, Berkeley Heights, N.J., assiguor to Esso Research and Engineering Company, a corporation of Delaware I Filed Sept. 22, 1958, Ser. No. 762,392 6-Claims. (Cl. 208-216) The present invention is concerned with an improved integrated hydrofining process for the production of high quality petroleum oil products. The invention is more particularly concerned with an improved integrated hydrofining process for the removal of sulfur from high quality petroleum oil products boiling in the middle distillate range.

The prior art is familiar with hydrofining processes used to improve the quality of petroleum products, particularly petroleum distillates. The hydrofining process is used to reduce the sulfur content and to improve other qualities of the oil. sweetening is the term applied to distillate treating processes which remove objectionable odors arising from the presence of mercaptans. Sweetening can be accomplished by oxidation of the mercaptans to non-odorous products, usually disulfides, or by an extraction process in which mercaptans are removed. At the present time, sweetening, in most large commercial refineries, is accomplished by chemical treating, such as the doctor sweetening process or the hypochlorite sweetening process, or by hydrofining.

In recent years, the use of hydrofining for diesel fuels has increased until now it has replaced the chemical treating processes for desulfurizing this high sulfur feed stock. But in the sweetening of other middle distillate feed stocks such as kerosene, jet fuel and hydrocarbon solvents boiling in the middle distillate range, the use of hydrofining has not found such wide recognition, primarily because the initial investment of a hydrofining unit to treat middle distillate fuels other than diesel fuels is much greater than for the conventional chemical sweetening processes.

The present invention reduces both the initial investment cost and the operating cost of a hydrofining process used for the sweetening of middle distillate stock by integrating the middle distillate hydrofining unit with a large diesel hydrofining unit found in most all modern refineries. The integrated process is especially valuable for use in refineries in which the volume of middle distillates treated approaches'approximately 50% of the volume of diesel oil treated. This integration, which is made possible by the use of mild sweetening conditions, permits the deletion of much of the equipment usually included in a conventional hydrofining process of this type, suchas furnaces, separators and recycle equipment. The integrated process, although providing heat to the smaller unit without the use of a second furnace, results in no net fuel consumption, since the heat used by the smaller unit is returned to the diesel hydrofining unit. By utilization of the present invention, the initial investment cost is reduced to a value comparable with that of hypo chlorite or doctor sweetening processes and the operating cost is reduced to a value substantially lower than for these chemical sweetening processes. The process of the present invention may be more fully understood by reference to the drawing illustrating one embodiment of the same.

Referring specifically to the drawing, which diagrammatically illustrates a preferred flow plan for the practice of this invention, a crude oil feed introduced by means of line 1 is fractionated in pipe still 2 and a middle distillate charge, i.e., jetfuel, boiling between 330 and 550 F., is removed while still hot from side stream stripper 3. The hot charge is transported by line 4 to heat exchanger 5, where the charge is heated to hydrofining temperature by exchange with the effluent from diesel fuel reactor 6 which is passed through heat exchanger 5 by means of line 7.

From heat exchanger 5, the hot charge is carried by means of line 8 to line 9 where hydrogen containing gas is introduced with the charge into reactor 10. In reactor 10, conditions which will be hereinafter described are maintained to accomplish the required sweetening of the middle distillate charge.

After being hydrofined in reactor 10, the middle dis tillate reactor effluent is passed to heat exchanger 13 where the efiluent is cooled by passing in heat exchange with the diesel feed which enters heat exchanger 13 and the diesel hydrofining process by means of line 14. From heat exchanger 13, the diesel feed passes to diesel reactor 6 by means of line 15, furnace 21 and line 12 where the heated feed contacts hydrogen-containing gas also entering diesel reactor 6 through line 12.

The middle distillate effluent cooled in heat exchanger 13 is then passed to stripper 17 by means of line 16. In stripper 17, steam is introduced through line 20 and light gases containing hydrogen sulfide, hydrogen, and light hydrocarbon gases are stripped off and taken overhead by line 18. The hydrofined middle distillate product is taken off at the bottom of stripper 17 through line 19.

Returning now to diesel reactor 6, the conditions which will be hereinafter described are maintained to produce a fully hydrofined diesel product. From reactor 6, the diesel reactor efliuent passes through line 7 through heat exchanger 5, where the hot effiuent is cooled, and thence into separator 22. In separator 22, hydrogen-containing gas is separated from the remaining mixture and part of it transported to reactor 10 by means of line 9, while any excess is discarded through line 36. If desired, the hydrogen containing gas may be passed through a conventional scrubber vessel (not shown) in which any impurities remaining after separation can be removed. The remaining mixture containing hydrogen sulfide and diesel oil product is removed to stripper 24 by line 23 where steam which is introduced into stripper 24 by means of line 26 is used to strip the hydrogen sulfide from the product. The hydrogen sulfide and light naphtha formed during hydrofining are removed overhead by line 28 while the diesel product is removed through line 27. The overhead vapors passing from stripper 24 by means of line 28 combine with the overhead vapors from stripper 17 in line 18 and are cooled in cooler 29 to condense out the naphtha. From cooler 29, the naphtha and hydrogen sulfide are passed to reflux drum 31 by line 30 where hydrogen sulfide is taken off overhead through line 31 and the naphtha, often referred to as wild naphtha, is removed by line 33. The naphtha may be returned to stripper 24 by line 34 or, preferably, sent to disposal by means of line 35.

The conditions in reactors 6 and 10 are set forth in In order to show the operating conditions and the heat exchange utilized by the present invention, the following example is set forth.

Example I A jet fuel feed boiling between 330 and 550 F, and a diesel fuel feed boiling between 350 and 700 F. may be sweetened according to the present invention using a cobalt molybdenum catalyst.

The jet fuel feed is taken directly from a pipe still at a temperature of 425 F. and passed in heat exchange with the diesel reactor effiuent which is at a temperature of 650 F. The temperature of the jet fuel feed will be increased to 525 F. while the temperature of the diesel reactor efiluent will be decreased to about 622 F.

After hydrofining the jet fuel feed at the preferred conditions of 500 F. at a pressure of 150 p.s.i.g., the jet fuel reactor efiluent having a temperature of 500 F. is passed in heat exchange with diesel feed entering the process. Temperature of the diesel feed is raised to 317 F. while the temperature of the jet fuel reactor effluent is decreased to 410 F. The diesel feed is then heated to the hydrofining temperature of 650 F. in a furnace.

After hydrofining and heat exchange, the diesel reactor effiuent is sent to a separator where hydrogen-containing gas is separated from the efiiuent at a temperature of 100 F. and a pressure of 180 p.s.i.g. and passed to the jet fuel reactor. The diesel reactor effluent is then sent to a stripper and the diesel product is removed from hydrogen-sulfide and light naphtha present in the effluent at a temperature of 415 F. and a pressure of 89 p.s.i.g.

The jet reactor efliuent, after heat exchange with the diesel fuel feed, is sent to a small stripper where the jet fuel product is removed from hydrogen sulfide and light naphtha present in the efiiuent at a temperature of 410 F. and a pressure of 85 p.s.i.g. The hydrogen sulfide and light naphtha are passed to a reflux drum which is operated in conjunction with the large diesel stripper where hydrogen sulfide is separated from the naphtha present at a temperature of 100 F. and a pressure of 83 p.s.i.g.

Although the diesel reactor is operated at conventional hydrofining conditions, it is necessary to operate the small hydrofining unit at very mild conditions independent of feed mercaptan number in order to obtain the advantages of this integrated process. The following example is set forth to show the results of operating under these conditions.

Example [I A middle distillate feed of Arabian wide-cut kerosene boiling from about 300 to 450 F. and containing 0.12 weight percent sulfur and a mercaptan number of 10.0 was sweetened in a hydrofining unit integrally connected to a large diesel hydrofining unit in accordance with this invention. The catalyst used was 4 wt. percent cobalt oxide and 13 wt. percent molybdenum oxide supported on an alumina base. The catalysts were used in the shape of A! pills. The hydrofining conditions were as follows:

Temperature, F 500 Pressure, p.s.i.g 120 Feed rate, v./hr./v 8 H feed rate, s.c.f./b 150 H consumption, s.c.f.'/b 5 H concentration in treat gas, percent 56 The kerosene product obtained contained 0.09 weight percent sulfur and had a mercaptan number ofonly 0.5.

The catalyst utilized in the present process may comprise known hydrofining catalyst. While the preferred catalyst for the diesel hydrofining reactor and the middle distillate hydrofining reactor is cobalt molybdate supported on alumina, the use of a specific hydrofining catalyst is not required or considered essential to the invention. In the preferred cobalt molybdate catalyst, the amount of cobalt oxide is about 2 to 5% and the amount of molybdenum oxide based on the weight of the catalyst is 7 to 14%. The catalyst may be prepared by any known method.

The catalyst, as it is employed in the present invention in either reactor, may be in the form of a fixed bed, a fluidized bed or a moving bed. It is contemplated that the process is best carried out by utilizing it in the form of a fixed bed. In this case it is desired that the catalyst carrier have a particle size of from about in. to V2 in. and preferably about /a inch. Particles of this nature may be prepared by conventional crushing, pilling and extruding processes or by other well known techniques. It has been found that a catalyst in the form of /s" diameter by A2" long pills afifords particularly satisfactory operation.

Regeneration of the catalyst may be required periodically, depending largely upon the nature of the feed. This regeneration is conveniently carried out at a temperature of about 900 F. with an oxygen containing gas.

The middle distillate feed stock to be used in the present invention is a hydrocarbon fraction boiling in the range of about 225 to 550 F. Specifically, the feed stock includes kerosene and jet fuel boiling between about 350 to 550 F. and hydrocarbon solvents boiling in the range of about 300 to 400 F.

To recapitulate, the present invention relates to improvements in the art of sweetening middle distillate feed stock by hydrofining. By maintaining mild conditions of temperature and pressure, it is possible to integrate the sweetening process with a large diesel hydrofining process and obtain the necessary economic advantage to make hydrofining preferable to the chemical sweetening process. By the use of the present invention, a furnace is eliminated with no loss of heat to the large unit, the use of expensive recycle equipment is reduced and other equipment is eliminated.

In regard to operating cost, the present invention enables the very great reduction of furnace fuel and cooling water requirements. This is especially important since previous economic studies comparing hydrofining of middle distillates with the chemical sweetening of this feed have shown that the costs of heating the feed to hydrofining temperatures and cooling the efiiuent for removal of hydrogen sulfide have made hydrofining costs higher than chemical sweetening costs.

A further advantage of this invention is the elimination of storage requirements for the sulfur containing middle distillate feed before hydrofining. A problem often encountered in conventional hydrofining operation is the fouling of preheat exchangers due to oxygen combining with the feed during tank storage. In conventional operations, in order to prevent this fouling, it is necessary to blanket the feed while in the storage tanks with inert oxygen-free gas. This is'both troublesome and expensive. By the very nature of the present invention, feed tankage is not necessary, and oxygen fouling of the preheat exchanges is completely eliminated.

It is understood that this invention is not limited to the specific examples which have been offered merely as illustrations and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

1. A continuous process which comprises hydrofining a diesel oil boiling in the range of about 350 to 700 F. in a first reactor vessel at temperatures in the range of from about 600-750 F. and at a pressure of from about -800 p.s.i.g., withdrawing a middle distillate charge boiling in the, range of about 225 to 55 0 F. directly from a pipe still, heating the middle distillate charge to hydrofining temperature as hereinafter defined by passing the middle distillate charge in indirect heat exchange with the hydrofined diesel oil efiiuent from said first reactor vessel, passing the cooled, hydrofined, diesel oil to a separator vessel, separating the hydrogen containing gas from the hydrofined diesel oil, passing the hydrogen containing gas to a second reactor vessel, passing the hydrofined diesel oil from the separator vessel to a first stripper vessel, stripping the hydrofined diesel oil free of hydrogen sulfide and light naphtha, withdrawing a diesel oil prod uct substantially free from sulfur from said first stripper vessel, passing the aforesaid preheated middle distillate stock in admixture with said hydrogen containing gas from said separator vessel over a hydrofining catalyst in said second reaction vessel at a temperature in the range of about 400 to 600 F. and a pressure in the range of about 75 to 400 p.s.i.g., cooling the hydrofined middle distillate efiluent from the second reactor vessel by passing it in indirect heat exchange with diesel oil feed, further heating the diesel oil feed to hydrofining temperature and charging it to said first reactor vessel.

2. A continuous process which comprises hydrofining a diesel oil boiling in the range of about 350 to 700 F. in a first reactor vessel at temperatures in the range of from about 600-750 F. and at a pressure of from about 150-800 p.s.i.g., withdrawing a middle distillate charge boiling in the range of about 225 to 550 F. directly from a pipe still, heating the middle distillate charge to hydrofining temperature as hereinafter defined by passing the middle distillate charge in indirect heat exchange with the hydrofined diesel oil efiiuent from said first reactor vessel, passing the cooled, hydrofined, diesel oil to a separator vessel, separating the hydrogen containing gas from the hydrofined diesel oil, passing the hydrogen containing gas to a second reactor vessel, passing the hydrofined diesel oil from the separator vessel to a first stripper ves- Bil sel, stripping the hydrofined diesel oil free of hydrogen sulfide and light naphtha, withdrawing a diesel oil product substantially free from sulfur from said first stripper vessel, passing the aforesaid preheated middle distillate stock in admixture with said hydrogen containing gas from said separator vessel over a hydrofining catalyst in said second reactor vessel at a temperature in the range of about 400 to 600 F. and a pressure in the range of about 75 to 400 p.s.i.g., cooling the hydrofined middle distillate efiiuent from the second reactor vessel by passing it in indirect heat exchange with diesel oil feed, further heating the diesel oil feed to hydrofining temperature and charging it to said first reactor vessel, passing the hydrofined middle distillate to a second stripper vessel, stripping light naphtha, hydrogen and hydrogen suliide from the hydrofined middle distillate, passing the light naphtha, hydrogen and hydrogen sulfide from the second stripper vessel to the first stripper vessel, and withdrawing from the second stripper vessel a middle distillate product substantially free of mercaptan sulfur.

3. The process of claim 2 in which the hydrofining catalyst used in the second reactor vessel is cobalt molybdate supported on alumina.

4. The process of claim 3 in which the middle distillate stock is kerosene boiling in the range of about 350 to 550 F.

5. The process of claim 3 in which the middle distillate stock is jet fuel boiling in a range of about 350 to 550 F.

6. The process of claim 3 in which the middle distillate stock is a hydrocarbon solvent boiling in the range of 300 to 400 F.

References Qited in the file of this patent UNITED STATES PATENTS 

1. A CONTINUOUS PROCESS WHICH COMPRISES HYDROFINING A DIESEL OIL BOILING IN THE RANGE OF ABOUT 350 TO 700*F. IN A FIRST REACTOR VESSEL AT TEMPERATURES IN THE RANGE OF FROM ABOUT 600-750*F. AND AT A PRESSURE OF FROM ABOUT 150-800 P.S.I.G., WITHDRAWING A MIDDLE DISTILLATE CHARGE BOILING IN THE RANGE OF ABOUT 225 TO 550*F. DIRECTLY FROM A PIPE STILL, HEATING THE MIDDLE DISTILLATE CHARGE TO HYDROFINING TEMPERATURE AS HEREINAFTER DEFINED BY PASSING THE MIDDLE DISTILLATE CHARGE IN INDIRECT HEAT EXCHANGE WITH THE HYDROFINED DIESEL OIL EFFLUENT FROM SAID FIRST REACTOR VESSEL, PASSING THE COOLED, HYDROFINED, DIESEL OIL TO A SEPARATOR VESSEL, SEPARATING THE HYDROGEN CONTAINING GAS FROM THE HYDROFINED DIESEL OIL, PASSING THE HYDROGEN CONTAINING GAS TO A SECOND REACTOR VESSEL, PASSING THE HYDROFINED DIESEL OIL FROM THE SEPARATOR VESSEL TO A FIRST STRIPPER VESSEL, STRIPPING THE HYDROFINED DIESEL OIL FREE OF HYDROGEN SULFIDE AND LIGHT NAPHTHA, WITHDRAWING A DIESEL OIL PRODUCT SUBSTANTIALLY FREE FROM SULFUR FROM SAID FIRST STRIPPER VESSEL, PASSING THE AFORESAID PREHEATED MIDDLE DISTILLATE STOCK IN ADMIXTURE WITH SAID HYDROGEN CONTAINING GAS FROM SAID SEPARATOR VESSEL OVER A HYDROFINING CATALYST IN SAID SECOND REACTION VESSEL AT A TEMPERATURE IN THE RANGE OF ABOUT 400 TO 600*F. AND A PRESSURE IN THE RANGE OF ABOUT 75 TO 400 P.S.I.G., COOLING THE HYDROFINED MIDDLE DISTILLATE EFFLUENT FROM THE SECOND REACTOR VESSEL BY PASSING IT IN INDIRECT HEAT EXCHANGE WITH DIESEL OIL FEED, FURTHER HEATING THE DIESEL OIL FEED TO HYDROFINING TEMPERATURE AND CHARGING IT TO SAID FIRST REACTOR VESSEL. 